Whey protein supplementation accelerates satellite cell proliferation during recovery from eccentric exercise

Recovery during Successive 120-min Football Games: Results from the 120-min Placebo/Carbohydrate Randomized Controlled Trial

PURPOSE

This study aimed to examine the recovery kinetics (i.e., time-dependent changes) of performance-related variables between two 120-min male football games performed 3 d apart with and without carbohydrate supplementation.

METHODS

Twenty male players (20 ± 1 yr; body fat, 14.9% ± 5.1%; maximal oxygen consumption, 59.4 ± 3.7 mL·kg -1 ·min -1 ) participated in two 120-min football games (G1, G2) according to a randomized, two-trial, repeated-measures, crossover, double-blind design. Participants received carbohydrate/placebo supplements during recovery between games. Field activity was monitored during the games. Performance testing and blood sampling were performed before and at 90 and 120 min of each game. Muscle biopsies were collected at baseline and at 90 and 120 min of G1 and pre-G2.

RESULTS

Compared with G1, G2 was associated with reduced total distance (10,870 vs 10,685 m during 90 min and 3327 vs 3089 m during extra 30 min; P = 0.007-0.038), average (6.7 vs 6.2 km/h during extra 30-min game-play; P = 0.007) and maximal speed (32.2 vs 30.2 km/h during 90 min and 29.0 vs 27.9 km/h during extra 30 min; P < 0.05), accelerations/decelerations ( P < 0.05), and mean heart rate ( P < 0.05). Repeated sprint ability ( P < 0.001), jumping ( P < 0.05), and strength ( P < 0.001) performance were compromised before and during G2. Muscle glycogen was not restored at G2 baseline ( P = 0.005). Extended game-play reduced lymphocyte, erythrocyte counts, hematocrit, hemoglobin, reduced glutathione ( P < 0.05) and increased delayed onset of muscle soreness, creatine kinase activity, blood glycerol, ammonia, and protein carbonyls ( P < 0.05) before and during G2. Pax7 + ( P = 0.004) and MyoD + cells ( P = 0.019) increased at baseline G2. Carbohydrate supplementation restored performance and glycogen, reduced glycerol and delayed onset of muscle soreness responses, and increased leukocyte counts and Pax7 + and MyoD + cells.

CONCLUSIONS

Results suggest that extended football games induce a prolonged recovery of performance, which may be facilitated by carbohydrate supplementation during a congested game fixture.

Molecular clocks, satellite cells, and skeletal muscle regeneration

Skeletal muscle comprises approximately 50% of individual body mass and plays vital roles in locomotion, heat production, and whole body metabolic homeostasis. This tissue exhibits a robust diurnal rhythm that is under control of the suprachiasmatic nucleus (SCN) region of the hypothalamus. The SCN acts as a "central" coordinator of circadian rhythms, while cell-autonomous "peripheral" clocks are located within almost all other tissues/organs in the body. Synchronization of the peripheral clocks in muscles (and other tissues) together with the central clock is crucial to ensure temporally coordinated physiology across all organ systems. By virtue of its mass, human skeletal muscle contains the largest collection of peripheral clocks, but within muscle resides a local stem cell population, satellite cells (SCs), which have their own functional molecular clock, independent of the numerous muscle clocks. Skeletal muscle has a daily turnover rate of 1%-2%, so the regenerative capacity of this tissue is important for whole body homeostasis/repair and depends on successful SC myogenic progression (i.e., proliferation, differentiation, and fusion). Emerging evidence suggests that SC-mediated muscle regeneration may, in part, be regulated by molecular clocks involved in SC-specific diurnal transcription. Here we provide insights on molecular clock regulation of muscle regeneration/repair and provide a novel perspective on the interplay between SC-specific molecular clocks, myogenic programs, and cell cycle kinetics that underpin myogenic progression.

Pax7+ Satellite Cells in Human Skeletal Muscle After Exercise: A Systematic Review and Meta-analysis

BACKGROUND

Skeletal muscle has extraordinary regenerative capabilities against challenge, mainly owing to its resident muscle stem cells, commonly identified by Pax7⁺, which expediently donate nuclei to the regenerating multinucleated myofibers. This local reserve of stem cells in damaged muscle tissues is replenished by undifferentiated bone marrow stem cells (CD34⁺) permeating into the surrounding vascular system.

OBJECTIVE

The purpose of the study was to provide a quantitative estimate for the changes in Pax7⁺ muscle stem cells (satellite cells) in humans following an acute bout of exercise until 96 h, in temporal relation to circulating CD34⁺ bone marrow stem cells. A subgroup analysis of age was also performed.

METHODS

Four databases (Web of Science, PubMed, Scopus, and BASE) were used for the literature search until February 2022. Pax7⁺ cells in human skeletal muscle were the primary outcome. Circulating CD34⁺ cells were the secondary outcome. The standardized mean difference (SMD) was calculated using a random-effects meta-analysis. Subgroup analyses were conducted to examine the influence of age, training status, type of exercise, and follow-up time after exercise.

RESULTS

The final search identified 20 studies for Pax7⁺ cells comprising a total of 370 participants between the average age of 21 and 74 years and 26 studies for circulating CD34⁺ bone marrow stem cells comprising 494 participants between the average age of 21 and 67 years. Only one study assessed Pax7⁺ cells immediately after aerobic exercise and showed a 32% reduction in exercising muscle followed by a fast repletion to pre-exercise level within 3 h. A large effect on increasing Pax7⁺ cell content in skeletal muscles was observed 24 h after resistance exercise (SMD = 0.89, p < 0.001). Pax7⁺ cells increased to ~ 50% above pre-exercise level 24-72 h after resistance exercise. For a subgroup analysis of age, a large effect (SMD = 0.81, p < 0.001) was observed on increasing Pax7⁺ cells in exercised muscle among adults aged > 50 years, whereas adults at younger age presented a medium effect (SMD = 0.64, p < 0.001). Both resistance exercise and aerobic exercise showed a medium overall effect in increasing circulating CD34⁺ cells (SMD = 0.53, p < 0.001), which declined quickly to the pre-exercise baseline level after exercise within 6 h.

CONCLUSIONS

An immediate depletion of Pax7⁺ cells in exercising skeletal muscle concurrent with a transient release of CD34⁺ cells suggest a replenishment of the local stem cell reserve from bone marrow. A protracted Pax7⁺ cell expansion in the muscle can be observed during 24-72 h after resistance exercise. This result provides a scientific basis for exercise recommendations on weekly cycles allowing for adequate recovery time. Exercise-induced Pax7⁺ cell expansion in muscle remains significant at higher age, despite a lower stem cell reserve after age 50 years. More studies are required to confirm whether Pax7⁺ cell increment can occur after aerobic exercise.

CLINICAL TRIAL REGISTRATION

Registered at the International Prospective Register of Systematic Reviews (PROSPERO) [identification code CRD42021265457].

The impact of dietary protein supplementation on recovery from resistance exercise-induced muscle damage: A systematic review with meta-analysis

BACKGROUND

It is unknown whether dietary protein consumption can attenuate resistance exercise-induced muscle damage (EIMD). Managing EIMD may accelerate muscle recovery and allow frequent, high-quality exercise to promote muscle adaptations. This systematic review and meta-analysis examined the impact of peri-exercise protein supplementation on resistance EIMD.

METHODS

A literature search was conducted on PubMed, SPORTDiscus, and Web of Science up to March 2021 for relevant articles. PEDro criteria were used to assess bias within included studies. A Hedges' g effect size (ES) was calculated for indirect markers of EIMD at  h post-exercise. Weighted ESs were included in a random effects model to determine overall ESs over time.

RESULTS

Twenty-nine studies were included in the systematic review and 40 trials were included in ≥1 meta-analyses (16 total). There were significant overall effects of protein for preserving isometric maximal voluntary contraction (MVC) at 96 h (0.563 [0.232, 0.894]) and isokinetic MVC at 24 h (0.639 [0.116, 1.162]), 48 h (0.447 [0.104, 0.790]), and 72 h (0.569 [0.136, 1.002]). Overall ESs were large in favour of protein for attenuating creatine kinase concentration at 48 h (0.836 [-0.001, 1.673]) and 72 h (1.335 [0.294, 2.376]). Protein supplementation had no effect on muscle soreness compared with the control.

CONCLUSION

Peri-exercise protein consumption could help maintain maximal strength and lower creatine kinase concentration following resistance exercise but not reduce muscle soreness. Conflicting data may be due to methodological divergencies between studies. Standardised methods and data reporting for EIMD research are needed.

Spirulina supplementation prevents exercise-induced lipid peroxidation, inflammation and skeletal muscle damage in elite rugby players

BACKGROUND

The present study aimed to examine the effects of spirulina supplementation on pro/antioxidant status, inflammation and skeletal muscle damage markers immediately and 24 h after exhaustive exercise in elite rugby players.

METHODS

Seventeen elite male Rugby Union players were randomly assigned to a spirulina (SPI: n = 9) or placebo (PLA: n = 8) group in a double-blind design. Subjects were supplemented with Spirulina platensis (5.7 g day^-1 ) or placebo (isoproteic and caloric) for 7 weeks. At baseline and after 7 weeks of supplementation, blood samples were obtained before (T0), immediately after (T1) and 24 h after (T2) exhaustive exercise. The Yoyo Intermittent Recovery Test Level 2 was used as an exhaustive exercise to induce oxidative stress (OS), inflammation and skeletal muscle damage. The studied parameters included pro/antioxidant status markers (superoxide dismutase, glutathione peroxidase, reduced glutathione/glutathione disulphide ratio, oxidised low-density lipoprotein and F2α-isoprostanes [F2-Isop]), inflammation markers (myeloperoxidase and C-reactive protein [CRP]) and skeletal muscle damage markers (lactate dehydrogenase and creatine kinase [CK]).

RESULTS

Our results showed that F2-Isop, CRP and CK levels significantly increased at T1 only in the PLA group (p < 0.05, p < 0.05 and p < 0.001, respectively) with no change in the SPI group, which reflects the effect of spirulina to prevent lipid peroxidation, inflammation and skeletal muscle damage induced by exhaustive exercise. Moreover, spirulina supplementation accelerated the return to baseline values given that F2-Isop, CRP and CK levels at T2 were significantly lower than at T0 in the SPI group (p < 0.05, p < 0.01 and p < 0.001, respectively).

CONCLUSIONS

Based on the markers used in the present study, our results show that spirulina supplementation potentially prevents exercise-induced lipid peroxidation, inflammation and skeletal muscle damage, and may also accelerate the recovery of some of these markers. Based on our findings, we recommend spirulina supplementation especially for those athletes who do not achieve the recommended antioxidant dietary intake and who perform a high training load aiming to reduce the magnitude of OS, inflammation and skeletal muscle damage, which could help to reduce performance losses and accelerate recovery after training/competitions throughout the season.

Sex differences in the impact of resistance exercise load on muscle damage: A protocol for a randomised parallel group trial

Introduction

Resistance training can induce skeletal muscle hypertrophy and strength gains, but is also associated with acute muscle damage, characterised by muscle soreness, impaired muscle function, and structural damage to muscle cell membranes and its components. These consequences can be detrimental to future exercise performance and dampen long-term training adaptations. Previous research has considered resistance exercise intensity as a factor in exercise-induced muscle damage (EIMD), though a clear direction of the findings has not yet been established. Further, female populations are heavily underrepresented in this field of study. Therefore, we here propose a study protocol designed to examine sex differences in the muscle damage response to resistance exercise performed with low or high loads in a population of untrained, young adults.

Methods

This study will employ a randomised parallel group design. Twenty-four males and 24 females will perform an acute leg-based resistance exercise session at either 30% (low-load) or 80% (high-load) of their pre-determined one-repetition maximum (1RM). Maximal leg strength will be determined by a 1RM test 3 wk before and 72 and 168 h after the exercise bout. Additionally, muscle damage will be assessed immediately before the exercise bout and immediately, 24, 48, 72, and 168 h after the exercise bout through measures of muscle soreness, limb circumference, range of motion, and serum concentrations of creatine kinase and interleukin-6. The outcomes of this trial could inform sex-specific resistance training recommendations and help bridge the sex data gap in sport and exercise science research.

Nutritional Regulation of Muscle Stem Cells in Exercise and Disease: The Role of Protein and Amino Acid Dietary Supplementation

Human skeletal muscle is a remarkedly plastic tissue that has a high capacity to adapt in response to various stimuli. These adaptations are due in part to the function of muscle-resident stem/progenitor cells. Skeletal muscle regeneration and adaptation is facilitated by the activation and expansion of muscle stem cells (MuSCs). MuSC fate is regulated by signals released from cells in their niche, such as fibro-adipogenic progenitors (FAPs), as well as a variety of non-cellular niche components. Sufficient dietary protein consumption is critical for maximizing skeletal muscle adaptation to exercise and maintaining skeletal muscle in disease; however, the role of dietary protein in altering MuSC and FAP responses to exercise in healthy populations and skeletal muscle disease states requires more research. The present review provides an overview of this emerging field and suggestions for future directions. The current literature suggests that in response to resistance exercise, protein supplementation has been shown to increase MuSC content and the MuSC response to acute exercise. Similarly, protein supplementation augments the increase in MuSC content following resistance training. Endurance exercise, conversely, is an area of research that is sparse with respect to the interaction of protein supplementation and exercise on muscle stem/progenitor cell fate. Initial evidence suggests that protein supplementation augments the early myogenic response to acute endurance exercise but does not enhance the MuSC response to endurance training. Resistance training increases the number of proliferating FAPs with no additional effect of protein supplementation. Future research should continue to focus on the nutritional regulation of skeletal muscle stem/progenitor cell fate paired with studies examining the effects of exercise on a variety of human populations.

Sex-Based Differences in the Myogenic Response and Inflammatory Gene Expression Following Eccentric Contractions in Humans

After muscle injury, the interaction between muscle satellite cells (SC) and the immune response is instrumental for the repair and regeneration of skeletal muscle tissue. Studies have reported sex-based differences in the skeletal muscle inflammatory and regenerative response following injury. However, many of these studies investigated such differences by manipulating the concentration of estradiol, in rodents and humans, without directly comparing males to females. We sought to explore differences in the myogenic and inflammatory response following unaccustomed eccentric exercise in males and females. We hypothesized that females would have a blunted myogenic and inflammatory response as compared to males.

Methods: 26 (13 male, 13 female) healthy young adults (22 ± 0.4 years [mean ± SEM]) performed 300 maximal eccentric contractions (180°/s) of the knee extensors. Muscle biopsies were taken before (pre) and 48 h (post) following eccentric damage. SC content and activation were determined by immunohistochemical and real time-polymerase chain reaction (rt-PCR) analysis. Inflammatory markers were analyzed using rt-PCR.

Results: Following eccentric damage, males had a greater expansion of type I-associated SC (p < 0.05), and there was a trend for a greater expansion in total SC (type I + II fibers) (p = 0.06) compared to females. There was a trend for a greater increase in Pax7 and CCL2 gene expression in males compared to females (p = 0.09).

Conclusion: We conclude that there are sex-based differences in the myogenic and inflammatory response, where females have a blunted SC and inflammatory response.

Reducing NF-κB Signaling Nutritionally is Associated with Expedited Recovery of Skeletal Muscle Function After Damage

CONTEXT

The early events regulating the remodeling program following skeletal muscle damage are poorly understood.

OBJECTIVE

The objective of this study was to determine the association between myofibrillar protein synthesis (myoPS) and nuclear factor-kappa B (NF-κB) signaling by nutritionally accelerating the recovery of muscle function following damage.

DESIGN, SETTING, PARTICIPANTS, AND INTERVENTIONS

Healthy males and females consumed daily postexercise and prebed protein-polyphenol (PP; n = 9; 4 females) or isocaloric maltodextrin placebo (PLA; n = 9; 3 females) drinks (parallel design) 6 days before and 3 days after 300 unilateral eccentric contractions of the quadriceps during complete dietary control.

MAIN OUTCOME MEASURES

Muscle function was assessed daily, and skeletal muscle biopsies were taken after 24, 27, and 36 hours for measurements of myoPS rates using deuterated water, and gene ontology and NF-κB signaling analysis using a quantitative reverse transcription PCR (RT-qPCR) gene array.

RESULTS

Eccentric contractions impaired muscle function for 48 hours in PLA intervention, but just for 24 hours in PP intervention (P = 0.047). Eccentric quadricep contractions increased myoPS compared with the control leg during postexercise (24-27 hours; 0.14 ± 0.01 vs 0.11 ± 0.01%·h-1, respectively; P = 0.075) and overnight periods (27-36 hours; 0.10 ± 0.01 vs 0.07 ± 0.01%·h-1, respectively; P = 0.020), but was not further increased by PP drinks (P > 0.05). Protein-polyphenol drinks decreased postexercise and overnight muscle IL1R1 (PLA = 2.8 ± 0.4, PP = 1.1 ± 0.4 and PLA = 1.9 ± 0.4, PP = 0.3 ± 0.4 log2 fold-change, respectively) and IL1RL1 (PLA = 4.9 ± 0.7, PP = 1.6 ± 0.8 and PLA = 3.7 ± 0.6, PP = 0.7 ± 0.7 log2 fold-change, respectively) messenger RNA expression (P < 0.05) and downstream NF-κB signaling compared with PLA.

CONCLUSION

Protein-polyphenol drink ingestion likely accelerates recovery of muscle function by attenuating inflammatory NF-κB transcriptional signaling, possibly to reduce aberrant tissue degradation rather than increase myoPS rates.

The role of protein hydrolysates for exercise-induced skeletal muscle recovery and adaptation: a current perspective

The protein supplement industry is expanding rapidly and estimated to have a multi-billion market worth. Recent research has centred on understanding how the manufacturing processes of protein supplements may impact muscle recovery and remodeling. The hydrolysed forms of protein undergo a further heating extraction process during production which may contribute to amino acids (AA) appearing in circulation at a slightly quicker rate, or greater amplitude, than the intact form. Whilst the relative significance of the rate of aminoacidemia to muscle protein synthesis is debated, it has been suggested that protein hydrolysates, potentially through the more rapid delivery and higher proportion of di-, tri- and smaller oligo-peptides into circulation, are superior to intact non-hydrolysed proteins and free AAs in promoting skeletal muscle protein remodeling and recovery. However, despite these claims, there is currently insufficient evidence to support superior muscle anabolic properties compared with intact non-hydrolysed proteins and/or free AA controls. Further research is warranted with appropriate protein controls, particularly in populations consuming insufficient amounts of protein, to support and/or refute an important muscle anabolic role of protein hydrolysates. The primary purpose of this review is to provide the reader with a current perspective on the potential anabolic effects of protein hydrolysates in individuals wishing to optimise recovery from, and maximise adaptation to, exercise training.

Effect of whey vs. soy protein supplementation on recovery kinetics following speed endurance training in competitive male soccer players: a randomized controlled trial

Background

Soccer-specific speed-endurance training induces short-term neuromuscular fatigue and performance deterioration over a 72-h recovery period, associated with elevated markers of exercise-induced muscle damage. We compared the effects of whey vs. soy protein supplementation on field activity, performance, muscle damage and redox responses following speed-endurance training in soccer players.

Methods

Ten well-trained, male soccer players completed three speed-endurance training trials, receiving whey protein (WP), soy protein (SP) or an isoenergetic placebo (PL; maltodextrin) according to a randomized, double-blind, crossover, repeated-measures design. A pre-loading period was applied in each trial during which protein supplementation was individually adjusted to reach a total protein intake of 1.5 g/kg/day, whereas in PL protein intake was adjusted at 0.8–1 g/kg/day. Following pre-loading, two speed-endurance training sessions (1 and 2) were performed 1 day apart, over a 3-day experimental period. During each session, field activity and heart rate were continuously monitored using global positioning system and heart rate monitors, respectively. Performance (isokinetic strength of knee extensors and flexors, maximal voluntary isometric contraction, speed, repeated sprint ability, countermovement jump), muscle damage (delayed-onset of muscle soreness, creatine kinase activity) and redox status (glutathione, total antioxidant capacity, protein carbonyls) were evaluated at baseline (pre), following pre-loading (post-load), and during recovery from speed-endurance training.

Results

High-intensity and high-speed running decreased (P ≤ 0.05) during speed-endurance training in all trials, but WP and SP mitigated this response. Isokinetic strength, maximal voluntary isometric contraction, 30-m speed, repeated sprint ability and countermovement jump performance were similarly deteriorated during recovery following speed-endurance training in all trials (P ≤ 0.05). 10 m speed was impaired at 24 h only in PL. Delayed-onset of muscle soreness, creatine kinase, total antioxidant capacity and protein carbonyls increased and glutathione decreased equally among trials following speed-endurance training (P ≤ 0.05), with SP inducing a faster recovery of protein carbonyls only at 48 h (P ≤ 0.05) compared to WP and PL.

Conclusions

In conclusion, increasing daily protein intake to 1.5 g/kg through ingestion of either whey or soy protein supplements mitigates field performance deterioration during successive speed-endurance training sessions without affecting exercise-induced muscle damage and redox status markers.

Trial registration

Name of the registry: clinicaltrials.gov. Trial registration: NCT03753321. Date of registration: 12/10/2018.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12970-021-00420-w.

Improved recovery from skeletal muscle damage is largely unexplained by myofibrillar protein synthesis or inflammatory and regenerative gene expression pathways

The contribution of myofibrillar protein synthesis (MyoPS) to recovery from skeletal muscle damage in humans is unknown. Recreationally active men and women consumed a daily protein-polyphenol beverage targeted at increasing amino acid availability and reducing inflammation (PPB; n = 9), both known to affect MyoPS, or an isocaloric placebo (PLA; n = 9) during 168 h of recovery from 300 maximal unilateral eccentric contractions (EE). Muscle function was assessed daily. Muscle biopsies were collected for 24, 27, 36, 72, and 168 h for MyoPS measurements using ²H₂O and expression of 224 genes using RT-qPCR and pathway analysis. PPB improved recovery of muscle function, which was impaired for 5 days after EE in PLA (interaction P < 0.05). Acute postprandial MyoPS rates were unaffected by nutritional intervention (24-27 h). EE increased overnight (27-36 h) MyoPS versus the control leg (PLA: 33 ± 19%; PPB: 79 ± 25%; leg P < 0.01), and PPB tended to increase this further (interaction P = 0.06). Daily MyoPS rates were greater with PPB between 72 and 168 h after EE, albeit after function had recovered. Inflammatory and regenerative signaling pathways were dramatically upregulated and clustered after EE but were unaffected by nutritional intervention. These results suggest that accelerated recovery from EE is not explained by elevated MyoPS or suppression of inflammation.NEW & NOTEWORTHY The present study investigated the contribution of myofibrillar protein synthesis (MyoPS) and associated gene signaling to recovery from 300 muscle-damaging, eccentric contractions. Measured with ²H₂O, MyoPS rates were elevated during recovery and observed alongside expression of inflammatory and regenerative signaling pathways. A nutritional intervention accelerated recovery; however, MyoPS and gene signaling were unchanged compared with placebo. These data indicate that MyoPS and associated signaling do not explain accelerated recovery from muscle damage.

The regulatory role of dietary factors in skeletal muscle development, regeneration and function

Skeletal muscle plays a crucial role in motor function, respiration, and whole-body energy homeostasis. How to regulate the development and function of skeletal muscle has become a hot research topic for improving lifestyle and extending life span. Numerous transcription factors and nutritional factors have been clarified are closely associated with the regulation of skeletal muscle development, regeneration and function. In this article, the roles of different dietary factors including green tea, quercetin, curcumin (CUR), eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and resveratrol (RES) in regulating skeletal muscle development, muscle mass, muscle function, and muscle recovery have been summarized and discussed. We also reviewed the potential regulatory molecular mechanism of these factors. Based on the current findings, dietary factors may be used as a potential therapeutic agent to treat skeletal muscle dysfunction as well as its related diseases.

The Effects of a High-Protein Diet on Markers of Muscle Damage Following Exercise in Active Older Adults: A Randomized, Controlled Trial

PURPOSE

This study examined whether a higher protein diet following strenuous exercise can alter markers of muscle damage and inflammation in older adults.

METHODS

Using a double-blind, independent group design, 10 males and eight females (age 57 ± 4 years; mass 72.3 ± 5.6 kg; height 1.7 ± 6.5 m) were supplied with a higher protein (2.50 g·kg-1·day-1) or moderate protein (1.25 g·kg-1·day-1) diet for 48 hr after 140 squats with 25% of their body mass. Maximal isometric voluntary contractions, muscle soreness, creatine kinase, Brief Assessment of Mood Adapted, and inflammatory markers were measured preexercise, and 24 hr and 48 hr postexercise.

RESULTS

The maximal isometric voluntary contractions decreased postexercise (p = .001, ηp2=.421), but did not differ between groups (p = .822, ηp2=.012). Muscle soreness peaked at 24 hr post in moderate protein (44 ± 30 mm) and 48 hr post in higher protein (70 ± 46 mm; p = .005; ηp2=.282); however, no group differences were found (p = .585; ηp2=.083). Monocytes and lymphocytes significantly decreased postexercise, and eosinophils increased 24 hr postexercise (p < 0.05), but neutrophils, creatine kinase, interleukin-6, C-reactive protein, monocyte chemotactic protein-1, and Brief Assessment of Mood Adapted were unchanged by exercise or the intervention (p > .05).

CONCLUSION

In conclusion, 2.50 g·kg-1·day-1 of protein is not more effective than 1.25 g·kg-1·day-1 for attenuating indirect markers of muscle damage and inflammation following strenuous exercise in older adults.

Dietary Intake and Nitrogen Balance in British Army Infantry Recruits Undergoing Basic Training

We assessed dietary intake and nitrogen balance during 14 weeks of Basic Training (BT) in British Army Infantry recruits. Nineteen men (mean ± SD: age 19.9 ± 2.6 years, height: 175.7 ± 6.5 cm, body mass 80.3 ± 10.1 kg) at the Infantry Training Centre, Catterick (ITC(C)) volunteered. Nutrient intakes and 24-h urinary nitrogen balance were assessed in weeks 2, 6 and 11 of BT. Nutrient intake was assessed using researcher-led weighed food records and food diaries, and Nutritics professional dietary software. Data were compared between weeks using a repeated-measures analysis of variance (ANOVA) with statistical significance set at p ≤ 0.05. There was a significant difference in protein intake (g) between weeks 2 and 11 of BT (115 ± 18 vs. 91 ± 20 g, p = 0.02, ES = 1.26). There was no significant difference in mean absolute daily energy (p = 0.44), fat (p = 0.79) or carbohydrate (CHO) intake (p = 0.06) between weeks. Nitrogen balance was maintained in weeks 2, 6 and 11, but declined throughout BT (2: 4.6 ± 4.1 g, 6: 1.6 ± 4.5 g, 11: -0.2 ± 5.5 g, p = 0.07). A protein intake of 1.5 g·kg^-1·d^-1 may be sufficient in the early stages of BT, but higher intakes may be individually needed later on in BT.

Satellite cells in ageing: use it or lose it

Individuals that maintain healthy skeletal tissue tend to live healthier, happier lives as proper muscle function enables maintenance of independence and actuation of autonomy. The onset of skeletal muscle decline begins around the age of 30, and muscle atrophy is associated with a number of serious morbidities and mortalities. Satellite cells are responsible for regeneration of skeletal muscle and enter a reversible non-dividing state of quiescence under homeostatic conditions. In response to injury, satellite cells are able to activate and re-enter the cell cycle, creating new cells to repair and create nascent muscle fibres while preserving a small population that can return to quiescence for future regenerative demands. However, in aged muscle, satellite cells that experience prolonged quiescence will undergo programmed cellular senescence, an irreversible non-dividing state that handicaps the regenerative capabilities of muscle. This review examines how periodic activation and cycling of satellite cells through exercise can mitigate senescence acquisition and myogenic decline.

The Effect of Whey Protein Supplementation on Myofibrillar Protein Synthesis and Performance Recovery in Resistance-Trained Men

BACKGROUND

The aim of this study was to investigate the effect of whey protein supplementation on myofibrillar protein synthesis (myoPS) and muscle recovery over a 7-d period of intensified resistance training (RT).

METHODS

In a double-blind randomised parallel group design, 16 resistance-trained men aged 18 to 35 years completed a 7-d RT protocol, consisting of three lower-body RT sessions on non-consecutive days. Participants consumed a controlled diet (146 kJ·kg^-1·d^-1, 1.7 g·kg^-1·d^-1 protein) with either a whey protein supplement or an isonitrogenous control (0.33 g·kg^-1·d^-1 protein). To measure myoPS, 400 ml of deuterium oxide (D₂O) (70 atom %) was ingested the day prior to starting the study and m. vastus lateralis biopsies were taken before and after RT-intervention. Myofibrillar fractional synthetic rate (myoFSR) was calculated via deuterium labelling of myofibrillar-bound alanine, measured by gas chromatography-pyrolysis-isotope ratio mass spectrometry (GC-Pyr-IRMS). Muscle recovery parameters (i.e., countermovement jump height, isometric-squat force, muscle soreness and serum creatine kinase) were assessed daily.

RESULTS

MyoFSR PRE was 1.6 (0.2) %∙d^-1 (mean (SD)). Whey protein supplementation had no effect on myoFSR (p = 0.771) or any recovery parameter (p = 0.390-0.989).

CONCLUSIONS

Over an intense 7-d RT protocol, 0.33 g·kg^-1·d^-1 of supplemental whey protein does not enhance day-to-day measures of myoPS or postexercise recovery in resistance-trained men.

Nutritional and Pharmacological Interventions to Expedite Recovery Following Muscle-Damaging Exercise in Older Adults: A Narrative Review of the Literature

Exercise-induced muscle damage (EIMD) manifests as muscle soreness, inflammation, and reductions in force generating capacity that can last for several days after exercise. The ability to recover and repair damaged tissues following EIMD is impaired with age, with older adults (≥50 years old) experiencing a slower rate of recovery than their younger counterparts do for the equivalent exercise bout. This narrative review discusses the literature examining the effect of nutritional or pharmacological supplements taken to counter the potentially debilitating effects of EIMD in older adults. Studies have assessed the effects of nonsteroidal anti-inflammatory drugs, vitamin C and/or E, or higher protein diets on recovery in older adults. Each intervention showed some promise for attenuating EIMD, but, overall, there is a paucity of available data in this population, and more studies are required to determine the influence of nutrition or pharmacological interventions on EIMD in older adults.

Comparison of ingesting a food bar containing whey protein and isomalto-oligosaccharides to carbohydrate on performance and recovery from an acute bout of resistance-exercise and sprint conditioning: an open label, randomized, counterbalanced, crossover pilot study

BACKGROUND

We previously reported that consuming a food bar (FB) containing whey protein and the plant fiber isomalto-oligosaccharides [IMO] had a lower glycemic (GI) but similar insulinemic response as a high GI carbohydrate. Therefore, we hypothesized that ingestion of this FB before, during, and following intense exercise would better maintain glucose homeostasis and performance while hastening recovery in comparison to the common practice of ingesting carbohydrate alone.

METHODS

Twelve resistance-trained males participated in an open label, randomized, counterbalanced, crossover trial with a 7-d washout period. Participants consumed a carbohydrate matched dextrose comparitor (CHO) or a FB containing 20 g of whey, 25 g of IMO, and 7 g of fat 30-min before, mid-way, and following intense exercise. Participants performed 11 resistance-exercises (3 sets of 10 repetitions at 70% of 1RM) followed by agility and sprint conditioning drills for time. Participants donated blood to assess catabolic and inflammatory markers, performed isokinetic strength tests, and rated perceptions of muscle soreness, hypoglycemia before, and following exercise and after 48 h of recovery. Data were analyzed using general linear models (GLM) for repeated measures and mean changes from baseline with 95% confidence intervals (CI) with a one-way analysis of variance. Data are reported as mean change from baseline with 95% CI.

RESULTS

GLM analysis demonstrated that blood glucose was significantly higher 30-min post-ingestion for CHO (3.1 [2.0, 4.3 mmol/L,] and FB (0.8 [0.2, 1.5, mmol/L, p = 0.001) while the post-exercise ratio of insulin to glucose was greater with FB (CHO 0.04 [0.00, 0.08], FB 0.11 [0.07, 0.15], p = 0.013, η² = 0.25). GLM analysis revealed no significant interaction effects between treatments in lifting volume of each resistance-exercise or total lifting volume. However, analysis of mean changes from baseline with 95% CI's revealed that leg press lifting volume (CHO -130.79 [- 235.02, - 26.55]; FB -7.94 [- 112.17, 96.30] kg, p = 0.09, η² = 0.12) and total lifting volume (CHO -198.26 [- 320.1, - 76.4], FB -81.7 [- 203.6, 40.1] kg, p = 0.175, η² = 0.08) from set 1 to 3 was significantly reduced for CHO, but not for the FB. No significant interaction effects were observed in ratings of muscle soreness. However, mean change analysis revealed that ratings of soreness of the distal vastus medialis significantly increased from baseline with CHO while being unchanged with FB (CHO 1.88 [0.60, 3.17]; FB 0.29 [- 0.99, 1.57] cm, p = 0.083, η² = 0.13). No significant GLM interaction or mean change analysis effects were seen between treatments in sprint performance, isokinetic strength, markers of catabolism, stress and sex hormones, or inflammatory markers.

CONCLUSION

Pilot study results provide some evidence that ingestion of this FB can positively affect glucose homeostasis, help maintain workout performance, and lessen perceptions of muscle soreness.

TRIAL REGISTRATION

clinicaltrials.gov, # NCT03704337 . Retrospectively registered 12, July 2018.

The redox-dependent regulation of satellite cells following aseptic muscle trauma (SpEED): study protocol for a randomized controlled trial

Background

Muscle satellite cells (SCs) are crucial for muscle regeneration following muscle trauma. Acute skeletal muscle damage results in inflammation and the production of reactive oxygen species (ROS) which may be implicated in SCs activation. Protection of these cells from oxidative damage is essential to ensure sufficient muscle regeneration. The aim of this study is to determine whether SCs activity under conditions of aseptic skeletal muscle trauma induced by exercise is redox-dependent.

Methods/design

Based on the SCs content in their vastus lateralis skeletal muscle, participants will be classified as either high or low respondents. In a randomized, double-blind, crossover, repeated-measures design, participants will then receive either placebo or N-acetylcysteine (alters redox potential in muscle) during a preliminary 7-day loading phase, and for eight consecutive days following a single bout of intense muscle-damaging exercise. In both trials, blood samples and muscle biopsies will be collected, and muscle performance and soreness will be measured at baseline, pre-exercise, 2 and 8 days post exercise. Biological samples will be analyzed for redox status and SCs activity. Between trials, a 4-week washout period will be implemented.

Discussion

This study is designed to investigate the impact of redox status on SCs mobilization and thus skeletal muscle potential for regeneration under conditions of aseptic inflammation induced by exercise. Findings of this trial should provide insight into (1) molecular pathways involved in SCs recruitment and muscle healing under conditions of aseptic skeletal muscle trauma present in numerous catabolic conditions and (2) whether skeletal muscle’s potential for regeneration depends on its basal SCs content.

Trial registration

ClinicalTrials.gov, ID: NCT03711838. Registered on 19 Oct 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3557-3) contains supplementary material, which is available to authorized users.

Cellular and morphological changes with EAA supplementation before and after total knee arthroplasty

Investigate the underlying cellular basis of muscle atrophy (Placebo) and atrophy reduction (essential amino acid supplementation, EAAs) in total knee arthroplasty (TKA) patients by examining satellite cells and other key histological markers of inflammation, recovery, and fibrosis. Forty-one subjects (53-76 yr) scheduled for TKA were randomized into two groups, ingesting 20 g of EAAs or placebo, twice-daily, for 7 days before TKA and for 6 wk after surgery. A first set of muscle biopsies was obtained from both legs before surgery in the operating room, and patients were randomly assigned and equally allocated to have two additional biopsies at either 1 or 2 wk after surgery. Biopsies were processed for gene expression and immunohistochemistry. Satellite cells were significantly higher in patients ingesting 20 g of essential amino acids twice daily for the 7 days leading up to surgery compared with Placebo (operative leg P = 0.03 for satellite cells/fiber and P = 0.05 for satellite cell proportions for Type I-associated cells and P = 0.05 for satellite cells/fiber for Type II-associated cells.) Myogenic regulatory factor gene expression was different between groups, with the Placebo Group having elevated MyoD expression at 1 wk and EAAs having elevated myogenin expression at 1 wk. M1 macrophages were more prevalent in Placebo than the EAAs Group. IL-6 and TNF-α transcripts were elevated postsurgery in both groups; however, TNF-α declined by 2 wk in the EAAs Group. EAAs starting 7 days before surgery increased satellite cells on the day of surgery and promoted a more favorable inflammatory environment postsurgery.NEW & NOTEWORTHY Clinical studies by our group indicate that the majority of muscle atrophy after total knee arthroplasty (TKA) in older adults occurs rapidly, within the first 2 wks. We have also shown that essential amino acid supplementation (EAAs) before and after TKA mitigates muscle atrophy; however, the mechanisms are unknown. These results suggest that satellite cell numbers are elevated with EAA ingestion before surgery, and after surgery, EAA ingestion positively influences markers of inflammation. Combined, these data may help inform further studies designed to address the accelerated sarcopenia that occurs in older adults after major surgery.

Hamstring rehabilitation in elite track and field athletes: applying the British Athletics Muscle Injury Classification in clinical practice

Rationale

Hamstring injuries are common in elite sports. Muscle injury classification systems aim to provide a framework for diagnosis. The British Athletics Muscle Injury Classification (BAMIC) describes an MRI classification system with clearly defined, anatomically focused classes based on the site of injury: (a) myofascial, (b) muscle–tendon junction or (c) intratendinous; and the extent of the injury, graded from 0 to 4. However, there are no clinical guidelines that link the specific diagnosis (as above) with a focused rehabilitation plan.

Objective

We present an overview of the general principles of, and rationale for, exercise-based hamstring injury rehabilitation in British Athletics. We describe how British Athletics clinicians use the BAMIC to help manage elite track and field athletes with hamstring injury. Within each class of injury, we discuss four topics: clinical presentation, healing physiology, how we prescribe and progress rehabilitation and how we make the shared decision to return to full training. We recommend a structured and targeted diagnostic and rehabilitation approach to improve outcomes after hamstring injury.

Molecular and cellular adaptations to exercise training in skeletal muscle from cancer patients treated with chemotherapy

BACKGROUND

A growing body of evidence suggests that exercise training has beneficial effects in cancer patients. The aim of the present study was to investigate the molecular basis underlying these beneficial effects in skeletal muscle from cancer patients.

METHODS

We investigated expression of selected proteins involved in cellular processes known to orchestrate adaptation to exercise training by western blot. Skeletal muscle biopsies were sampled from ten cancer patients before and after 4-7 weeks of ongoing chemotherapy, and subsequently after 10 weeks of continued chemotherapy in combination with exercise training. Biopsies from ten healthy matched subjects served as reference.

RESULTS

The expression of the insulin-regulated glucose transporter, GLUT4, increased during chemotherapy and continued to increase during exercise training. A similar trend was observed for ACC, a key enzyme in the biosynthesis and oxidation of fatty acids, but we did not observe any changes in other regulators of substrate metabolism (AMPK and PDH) or mitochondrial proteins (Cyt-C, COX-IV, SDHA, and VDAC). Markers of proteasomal proteolysis (MURF1 and ATROGIN-1) decreased during chemotherapy, but did not change further during chemotherapy combined with exercise training. A similar pattern was observed for autophagy-related proteins such as ATG5, p62, and pULK1 Ser⁷⁵⁷, but not ULK1 and LC3BII/LC3BI. Phosphorylation of FOXO3a at Ser^318/321 did not change during chemotherapy, but decreased during exercise training. This could suggest that FOXO3a-mediated transcriptional regulation of MURF1 and ATROGIN-1 serves as a mechanism by which exercise training maintains proteolytic systems in skeletal muscle in cancer patients. Phosphorylation of proteins that regulate protein synthesis (mTOR at Ser²⁴⁴⁸ and 4EBP1 at Thr^37/46) increased during chemotherapy and leveled off during exercise training. Finally, chemotherapy tended to increase the number of satellite cells in type 1 fibers, without any further change during chemotherapy and exercise training. Conversely, the number of satellite cells in type 2 fibers did not change during chemotherapy, but increased during chemotherapy combined with exercise training.

CONCLUSIONS

Molecular signaling cascades involved in exercise training are disturbed during cancer and chemotherapy, and exercise training may prevent further disruption of these pathways.

TRIAL REGISTRATION

The study was approved by the local Scientific Ethics Committee of the Central Denmark Region (Project ID: M-2014-15-14; date of approval: 01/27/2014) and the Danish Data Protection Agency (case number 2007-58-0010; date of approval: 01/28/2015). The trial was registered at http//www.clinicaltrials.gov (registration number: NCT02192216; date of registration 07/17-2014).

Pre-Bed Casein Protein Supplementation Does Not Enhance Acute Functional Recovery in Physically Active Males and Females When Exercise is Performed in the Morning

This study examined whether consuming casein protein (CP) pre-sleep could accelerate acute recovery following muscle-damaging exercise. Thirty-nine active males and females performed 100 drop jumps in the morning, consumed their habitual diet during the day, and then within 30 min pre-bed consumed either ~40 g of CP (n = 19) or ~40 g of a carbohydrate-only control (CON) (n = 20). Maximal isometric voluntary contractions (MIVC), countermovement jumps (CMJ), pressure-pain threshold (PPT), subjective muscle soreness and the brief assessment of mood adapted (BAM+) were measured pre, 24 and 48 h following the drop jumps. MIVC decreased in CP and CON post-exercise, peaking at 24 h post (CP: -8.5 ± 3.5 vs. CON: -13.0 ± 2.9%, respectively); however, no between-group differences were observed (p = 0.486; η_p² =0.02). There were also no group differences in the recovery of CMJ height, PPT and BAM+ (p > 0.05). Subjective muscle soreness increased post-exercise, but no group differences were present at 24 h (CP: 92 ± 31 mm vs. CON: 90 ± 46 mm) or 48 h (CP: 90 ± 44 mm vs. CON: 80 ± 58 mm) (p > 0.05). These data suggest that pre-bed supplementation with ~40 g of CP is no more beneficial than CON for accelerating the recovery following muscle-damaging exercise.

Myokines in Home-Based Functional Electrical Stimulation-Induced Recovery of Skeletal Muscle in Elderly and Permanent Denervation

Neuromuscular disorders, disuse, inadequate nutrition, metabolic diseases, cancer and aging produce muscle atrophy and this implies that there are different types of molecular triggers and signaling pathways for muscle wasting. Exercise and muscle contractions may counteract muscle atrophy by releasing a group of peptides, termed myokines, to protect the functionality and to enhance the exercise capacity of skeletal muscle. In this review, we are looking at the role of myokines in the recovery of permanent denervated and elderly skeletal muscle tissue. Since sub-clinical denervation events contribute to both atrophy and the decreased contractile speed of aged muscle, we saw a parallel to spinal cord injury and decided to look at both groups together. The muscle from lifelong active seniors has more muscle bulk and more slow fiber-type groupings than those of sedentary seniors, demonstrating that physical activity maintains slow motoneurons that reinnervate the transiently denervated muscle fibers. Furthermore, we summarized the evidence that muscle degeneration occur with irreversible Conus and Cauda Equina syndrome, a spinal cord injury in which the human leg muscles may be permanently disconnected from the peripheral nervous system. In these patients, suffering with an estreme case of muscle disuse, a complete loss of muscle fibers occurs within five to ten years after injury. Their recovered tetanic contractility, induced by home-based Functional Electrical Stimulation, can restore the muscle size and function in compliant Spinal Cord Injury patients, allowing them to perform electrical stimulation-supported stand-up training. Myokines are produced and released by muscle fibers under contraction and exert both local and systemic effects. Changes in patterns of myokine secretion, particularly of IGF-1 isoforms, occur in long-term Spinal Cord Injury persons and also in very aged people. Their modulation in Spinal Cord Injury and late aging are also key factors of home-based Functional Electrical Stimulation - mediated muscle recovery. Thus, Functional Electrical Stimulation should be prescribed in critical care units and nursing facilities, if persons are unable or reluctant to exercise. This will result in less frequent hospitalizations and a reduced burden on patients' families and public health services.

Ingestion of a Multi-Ingredient Supplement Does Not Alter Exercise-Induced Satellite Cell Responses in Older Men

Background

Nutritional supplementation can have beneficial effects on body composition, strength, and function in older adults. However, whether the response of satellite cells can be altered by nutritional supplementation in older adults remains unknown.

Objective

We assessed whether a multi-ingredient protein-based supplement taken over a prolonged period of time could alter the muscle satellite cell response after exercise in older men.

Methods

Twenty-seven older men [mean ± SD age: 73 ± 1 y; mean ± SD body mass index (kg/m2): 28 ± 1] participated in a randomized double-blind experiment. Participants were randomly divided into an experimental (EXP) group (n = 13) who consumed a multi-ingredient protein-based supplement [30 g whey protein, 2.5 g creatine, 500 IU vitamin D, 400 mg Ca, and 1500 mg n-3 (ω-3) polyunsaturated fatty acids] 2 times/d for 7 wk or a control (CON; 22 g maltodextrin) group (n = 14). After 7 wk of supplementation, all participants performed a single resistance exercise session, and muscle biopsy samples were taken from the vastus lateralis before and 24 and 48 h after exercise. Immunohistochemistry was used to assess the change in type I and II muscle fiber satellite cell content and activation status of the cells. In addition, mRNA expression of the myogenic regulatory factors was determined by using reverse transcriptase-polymerase chain reaction.

Results

In response to the single bout of exercise, type I muscle fiber satellite cell content was significantly increased at 24 h (0.132 ± 0.015 and 0.131 ± 0.011 satellite cells/fiber in CON and EXP groups, respectively) and 48 h (0.126 ± 0.010 and 0.120 ± 0.012 satellite cells/fiber in CON and EXP groups, respectively) compared with pre-exercise (0.092 ± 0.007 and 0.118 ± 0.017 satellite cells/fiber in CON and EXP groups, respectively) muscle biopsy samples (P < 0.01), with no difference between the 2 groups. In both groups, we observed no significant changes in type II muscle fiber satellite cell content after exercise.

Conclusion

Ingesting a multi-ingredient protein-based supplement for 7 wk did not alter the type I or II muscle fiber satellite cell response during postexercise recovery in older men. This trial was registered at www.clinicaltrials.gov as NCT02281331.

Post-Game High Protein Intake May Improve Recovery of Football-Specific Performance during a Congested Game Fixture: Results from the PRO-FOOTBALL Study

The effects of protein supplementation on performance recovery and inflammatory responses during a simulated one-week in-season microcycle with two games (G1, G2) performed three days apart were examined. Twenty football players participated in two trials, receiving either milk protein concentrate (1.15 and 0.26 g/kg on game and training days, respectively) (PRO) or an energy-matched placebo (1.37 and 0.31 g/kg of carbohydrate on game and training days, respectively) (PLA) according to a randomized, repeated-measures, crossover, double-blind design. Each trial included two games and four daily practices. Speed, jump height, isokinetic peak torque, and muscle soreness of knee flexors (KF) and extensors (KE) were measured before G1 and daily thereafter for six days. Blood was drawn before G1 and daily thereafter. Football-specific locomotor activity and heart rate were monitored using GPS technology during games and practices. The two games resulted in reduced speed (by 3–17%), strength of knee flexors (by 12–23%), and jumping performance (by 3–10%) throughout recovery, in both trials. Average heart rate and total distance covered during games remained unchanged in PRO but not in PLA. Moreover, PRO resulted in a change of smaller magnitude in high-intensity running at the end of G2 (75–90 min vs. 0–15 min) compared to PLA (P = 0.012). KE concentric strength demonstrated a more prolonged decline in PLA (days 1 and 2 after G1, P = 0.014–0.018; days 1, 2 and 3 after G2, P = 0.016–0.037) compared to PRO (days 1 after G1, P = 0.013; days 1 and 2 after G2, P = 0.014–0.033) following both games. KF eccentric strength decreased throughout recovery after G1 (PLA: P=0.001–0.047—PRO: P =0.004–0.22) in both trials, whereas after G2 it declined throughout recovery in PLA (P = 0.000–0.013) but only during the first two days (P = 0.000–0.014) in PRO. No treatment effect was observed for delayed onset of muscle soreness, leukocyte counts, and creatine kinase activity. PRO resulted in a faster recovery of protein and lipid peroxidation markers after both games. Reduced glutathione demonstrated a more short-lived reduction after G2 in PRO compared to PLA. In summary, these results provide evidence that protein feeding may more efficiently restore football-specific performance and strength and provide antioxidant protection during a congested game fixture.

Postexercise essential amino acid supplementation amplifies skeletal muscle satellite cell proliferation in older men 24 hours postexercise

Aged skeletal muscle has an attenuated and delayed ability to proliferate satellite cells in response to resistance exercise. The mechanistic target of rapamycin complex 1 (mTORC1) signaling pathway is a focal point for cell growth, however, the effect of postexercise mTORC1 activation on human skeletal muscle satellite cell (SC) proliferation is unknown. To test the proliferative capacity of skeletal muscle SC in aging muscle to a potent mTORC1 activator (i.e., EAA; essential amino acids) we recruited older (~72y) men to conduct leg resistance exercise (8setsx10reps) without (−EAA; n = 8) and with (+EAA: n = 11) ingestion of 10 g of EAA 1 h postexercise. Muscle biopsies were taken before exercise (Pre) and 24 h postexercise (Post) for assessment of expression and fiber type‐specific Pax7⁺SC, Ki67⁺Pax7⁺SC and MyoD⁺SC. −EAA did not show an increase in Pax7⁺ satellite cells at Post(P > 0.82). Although statistical significance for an increase in Pax7 +  SC at 24 h post‐RE was not observed in +EAA versus −EAA, we observed trends for a treatment difference (P < 0.1). When examining the change from Pre to Post trends were demonstrated (#/myofiber: P = 0.076; and %/myonuclei: P = 0.065) for a greater increase in +EAA versus −EAA. Notably, we found an increase SC proliferation in +EAA, but not −EAA with increase in Ki67⁺SC and MyoD⁺ cells (P < 0.05). Ki67⁺SC also exhibited a significant group difference Post (P < 0.010). Pax7⁺SC in fast twitch myofibers did not change and were not different between groups (P > 0.10). CDK2, MEF2C, RB1 mRNA only increased in +EAA (P < 0.05). Acute muscle satellite cell proliferative capacity may be partially rescued with postexercise EAA ingestion in older men.

Potential Roles of n-3 PUFAs during Skeletal Muscle Growth and Regeneration

Omega-3 polyunsaturated fatty acids (n-3 PUFAs), which are commonly found in fish oil supplements, are known to possess anti-inflammatory properties and more recently alter skeletal muscle function. In this review, we discuss novel findings related to how n-3 PUFAs modulate molecular signaling responsible for growth and hypertrophy as well as the activity of muscle stem cells. Muscle stem cells commonly known as satellite cells, are primarily responsible for driving the skeletal muscle repair process to potentially damaging stimuli, such as mechanical stress elicited by exercise contraction. To date, there is a paucity of human investigations related to the effects of n-3 PUFAs on satellite cell content and activity. Based on current in vitro investigations, this review focuses on novel mechanisms linking n-3 PUFA’s to satellite cell activity and how they may improve muscle repair. Understanding the role of n-3 PUFAs during muscle growth and regeneration in association with exercise could lead to the development of novel supplementation strategies that increase muscle mass and strength, therefore possibly reducing the burden of muscle wasting with age.

The Effect of Whey Protein Supplementation on the Temporal Recovery of Muscle Function Following Resistance Training: A Systematic Review and Meta-Analysis

Whey protein (WP) is a widely consumed nutritional supplement, known to enhance strength and muscle mass during resistance training (RT) regimens. Muscle protein anabolism is acutely elevated following RT, which is further enhanced by WP. As a result, there is reason to suggest that WP supplementation may be an effective nutritional strategy for restoring the acute loss of contractile function that occurs following strenuous RT. This systematic review and meta-analysis provides a synthesis of the literature to date, investigating the effect of WP supplementation on the recovery of contractile function in young, healthy adults. Eight studies, containing 13 randomised control trials (RCTs) were included in this review and meta-analysis, from which individual standardised effect sizes (ESs) were calculated, and a temporal overall ES was determined using a random-effects model. Whilst only half of the individual studies reported beneficial effects for WP, the high-quality evidence taken from the 13 RCTs was meta-analysed, yielding overall positive small to medium effects for WP from < 24 to 96 h (ES range = 0.4 to 0.7), for the temporal restoration of contractile function compared to the control treatment. Whilst the effects for WP were shown to be consistent over time, these results are limited to 13 RCTs, principally supporting the requirement for further comprehensive research in this area.

Impact of blood flow-restricted bodyweight exercise on skeletal muscle adaptations

This study ascertains the ability of bodyweight blood flow-restricted (BFR) exercise training to promote skeletal muscle adaptations of significance for muscle accretion and metabolism. Six healthy young individuals (three males and three females) performed six weeks of bodyweight BFR training. Each session consisted of five sets of sit-to-stand BFR exercise to volitional failure with 30-second inter-set recovery. Prior to, and at least 72 h after training, muscle biopsies were taken from m. vastus lateralis to assess changes in fibre type-specific cross-sectional area (CSA), satellite cell (SC) and myonuclei content and capillarization, as well as mitochondrial protein expression. Furthermore, magnetic resonance imaging was used to assess changes in whole thigh muscle CSA. Finally, isometric knee extensor muscle strength was evaluated. An increase in knee extensor whole muscle CSA was observed at middle and distal localizations after training (3·2% and 3·5%, respectively) (P<0·05), and a trend was observed towards an increase in type I fibre CSA, whereas muscle strength did not increase. Additionally, the number of SCs and myonuclei associated with type I fibres increased by 65·7% and 20%, respectively (P<0·05). No significant changes were observed in measures of muscle capillarization and mitochondrial proteins. In conclusion, six weeks of bodyweight-based BFR exercise promoted myocellular adaptations related to muscle accretion, but not metabolic properties. Moreover, the study revealed that an appropriate total training volume needs further investigation before recommending bodyweight BFR to patient populations.

Protein Supplementation Does Not Affect Myogenic Adaptations to Resistance Training

It has been proposed that protein supplementation during resistance exercise training enhances muscle hypertrophy. The degree of hypertrophy during training is controlled in part through the activation of satellite cells and myonuclear accretion.

PURPOSE

This study aimed to determine the efficacy of protein supplementation (and the type of protein) during traditional resistance training on myofiber cross-sectional area, satellite cell content, and myonuclear addition.

METHODS

Healthy young men participated in supervised whole-body progressive resistance training 3 d·wk for 12 wk. Participants were randomized to one of three groups ingesting a daily 22-g macronutrient dose of soy-dairy protein blend (PB, n = 22), whey protein isolate (WP, n = 15), or an isocaloric maltodextrin placebo (MDP, n = 17). Lean mass, vastus lateralis myofiber-type-specific cross-sectional area, satellite cell content, and myonuclear addition were assessed before and after resistance training.

RESULTS

PB and the pooled protein treatments (PB + WP = PRO) exhibited a greater whole-body lean mass %change compared with MDP (P = 0.057 for PB) and (P = 0.050 for PRO), respectively. All treatments demonstrated similar leg muscle hypertrophy and vastus lateralis myofiber-type-specific cross-sectional area (P < 0.05). Increases in myosin heavy chain I and II myofiber satellite cell content and myonuclei content were also detected after exercise training (P < 0.05).

CONCLUSION

Protein supplementation during resistance training has a modest effect on whole-body lean mass as compared with exercise training without protein supplementation, and there was no effect on any outcome between protein supplement types (blend vs whey). However, protein supplementation did not enhance resistance exercise-induced increases in myofiber hypertrophy, satellite cell content, or myonuclear addition in young healthy men. We propose that as long as protein intake is adequate during muscle overload, the adaptations in muscle growth and function will not be influenced by protein supplementation.

Murine myoblast migration: influence of replicative ageing and nutrition

Cell migration is central to skeletal muscle repair following damage. Leucine and β-Hydroxy β-methylbutyric acid (HMB) are supplements consumed for recovery from muscle damaging exercise in humans, however, their impact on muscle cell migration with age is not yet understood. We hypothesised that replicatively aged ("aged"; P46-P48) myoblasts would be less efficient at basal and supplemented repair versus parental controls ("control"; P12-P16). Aged and control myoblasts were scratch-damaged and migration velocity, directionality and distance assessed over 48 h in the absence and presence of leucine (10 mM) or HMB (10 mM) ± PI3K/Akt (LY294002 10 μM), ERK (PD98059 5 μM) or mTOR (rapamycin 0.5 μM) inhibition. Opposing our hypothesis, aged cells displayed increased velocities, directionality and distance migrated (P < 0.001) versus control. Leucine and HMB significantly increased (P < 0.001) the same parameters in control cells. The supplements were with smaller, albeit significant impact on aged cell velocity (P < 0.001) and in the presence of HMB only, distance (P = 0.041). Inhibitor studies revealed that, PI3K and ERK activation were essential for velocity, directionality and migration distance of aged cells in basal conditions, whereas mTOR was important for directionality only. While PI3K activation was critical for all parameters in control cells (P < 0.001), inhibition of ERK or mTOR improved, rather than reduced, control cell migration distance. Enhanced basal velocity, directionality and distance in aged cells required ERK and PI3K activation. By contrast, in control cells, basal migration was underpinned by PI3K activation, and facilitated by leucine or HMB supplementation, to migration levels seen in aged cells. These data suggest that replicatively aged myoblasts are not anabolically resistant per se, but are capable of efficient repair, underpinned by altered signaling pathways, compared with unaged control myoblasts.

Whey protein hydrolysate supplementation accelerates recovery from exercise-induced muscle damage in females

A number of different forms of protein and their analogues have been investigated for their efficacy in ameliorating exercise-induced muscle damage (EIMD) and recovery. Preliminary data regarding whey protein hydrolysate (WPH) supplementation are promising. However, its efficacy beyond acute eccentric/resistance exercise bouts or longer term training programmes are limited and all investigations have been conducted in male or mixed-sex groups. This study sought to elucidate whether the benefits of WPH previously reported can be demonstrated in females following repeated-sprint exercise. Twenty physically active females were assigned to consume 2 doses of 70 mL WPH or isoenergetic carbohydrate (CHO) for 4 days post-EIMD. Measures of muscle soreness, limb girth, flexibility, muscle function, and creatine kinase were collected before, immediately after, and 24, 48, and 72 h postexercise. Time effects were observed for all variables (p < 0.05) except limb girth, which is indicative of EIMD. Flexibility improved beyond baseline measures following WPH by 72 h, but had failed to recover in the CHO group (p = 0.011). Reactive strength index was higher throughout recovery in the WPH group compared with CHO (p = 0.016). Reductions in creatine kinase were greater following WPH compared with CHO at 48 h post-EIMD (p = 0.031). The findings suggest that 4-day supplementation of WPH is beneficial for reducing symptoms of EIMD and improving recovery of muscle function in physically active females.

Effects of Whey, Soy or Leucine Supplementation with 12 Weeks of Resistance Training on Strength, Body Composition, and Skeletal Muscle and Adipose Tissue Histological Attributes in College-Aged Males

We sought to determine the effects of L-leucine (LEU) or different protein supplements standardized to LEU (~3.0 g/serving) on changes in body composition, strength, and histological attributes in skeletal muscle and adipose tissue. Seventy-five untrained, college-aged males (mean ± standard error of the mean (SE); age = 21 ± 1 years, body mass = 79.2 ± 0.3 kg) were randomly assigned to an isocaloric, lipid-, and organoleptically-matched maltodextrin placebo (PLA, n = 15), LEU (n = 14), whey protein concentrate (WPC, n = 17), whey protein hydrolysate (WPH, n = 14), or soy protein concentrate (SPC, n = 15) group. Participants performed whole-body resistance training three days per week for 12 weeks while consuming supplements twice daily. Skeletal muscle and subcutaneous (SQ) fat biopsies were obtained at baseline (T1) and ~72 h following the last day of training (T39). Tissue samples were analyzed for changes in type I and II fiber cross sectional area (CSA), non-fiber specific satellite cell count, and SQ adipocyte CSA. On average, all supplement groups including PLA exhibited similar training volumes and experienced statistically similar increases in total body skeletal muscle mass determined by dual X-ray absorptiometry (+2.2 kg; time p = 0.024) and type I and II fiber CSA increases (+394 μm² and +927 μm²; time p < 0.001 and 0.024, respectively). Notably, all groups reported increasing Calorie intakes ~600–800 kcal/day from T1 to T39 (time p < 0.001), and all groups consumed at least 1.1 g/kg/day of protein at T1 and 1.3 g/kg/day at T39. There was a training, but no supplementation, effect regarding the reduction in SQ adipocyte CSA (−210 μm²; time p = 0.001). Interestingly, satellite cell counts within the WPC (p < 0.05) and WPH (p < 0.05) groups were greater at T39 relative to T1. In summary, LEU or protein supplementation (standardized to LEU content) does not provide added benefit in increasing whole-body skeletal muscle mass or strength above PLA following 3 months of training in previously untrained college-aged males that increase Calorie intakes with resistance training and consume above the recommended daily intake of protein throughout training. However, whey protein supplementation increases skeletal muscle satellite cell number in this population, and this phenomena may promote more favorable training adaptations over more prolonged periods.

Protein ingestion preserves proteasome activity during intense aseptic inflammation and facilitates skeletal muscle recovery in humans

The ubiquitin–proteasome system (UPS) is the main cellular proteolytic system responsible for the degradation of normal and abnormal (e.g. oxidised) proteins. Under catabolic conditions characterised by chronic inflammation, the UPS is activated resulting in proteolysis, muscle wasting and impaired muscle function. Milk proteins provide sulphur-containing amino acid and have been proposed to affect muscle inflammation. However, the response of the UPS to aseptic inflammation and protein supplementation is largely unknown. The aim of this study was to investigate how milk protein supplementation affects UPS activity and skeletal muscle function under conditions of aseptic injury induced by intense, eccentric exercise. In a double-blind, cross-over, repeated measures design, eleven men received either placebo (PLA) or milk protein concentrate (PRO, 4×20 g on exercise day and 20 g/d for the following 8 days), following an acute bout of eccentric exercise (twenty sets of fifteen eccentric contractions at 30°/s) on an isokinetic dynamometer. In each trial, muscle biopsies were obtained from the vastus lateralis muscle at baseline, as well as at 2 and 8 d post exercise, whereas blood samples were collected before exercise and at 6 h, 1 d, 2 d and 8 d post exercise. Muscle strength and soreness were assessed before exercise, 6 h post exercise and then daily for 8 consecutive days. PRO preserved chymotrypsin-like activity and attenuated the decrease of strength, facilitating its recovery. PRO also prevented the increase of NF-κB phosphorylation and HSP70 expression throughout recovery. We conclude that milk PRO supplementation following exercise-induced muscle trauma preserves proteasome activity and attenuates strength decline during the pro-inflammatory phase.

Recovery from muscle weakness by exercise and FES: lessons from Masters, active or sedentary seniors and SCI patients

Many factors contribute to the decline of skeletal muscle that occurs as we age. This is a reality that we may combat, but not prevent because it is written into our genome. The series of records from World Master Athletes reveals that skeletal muscle power begins to decline at the age of 30 years and continues, almost linearly, to zero at the age of 110 years. Here we discuss evidence that denervation contributes to the atrophy and slowness of aged muscle. We compared muscle from lifelong active seniors to that of sedentary elderly people and found that the sportsmen have more muscle bulk and slow fiber type groupings, providing evidence that physical activity maintains slow motoneurons which reinnervate muscle fibers. Further, accelerated muscle atrophy/degeneration occurs with irreversible Conus and Cauda Equina syndrome, a spinal cord injury in which the human leg muscles may be permanently disconnected from the nervous system with complete loss of muscle fibers within 5-8 years. We used histological morphometry and Muscle Color Computed Tomography to evaluate muscle from these peculiar persons and reveal that contraction produced by home-based Functional Electrical Stimulation (h-bFES) recovers muscle size and function which is reversed if h-bFES is discontinued. FES also reverses muscle atrophy in sedentary seniors and modulates mitochondria in horse muscles. All together these observations indicate that FES modifies muscle fibers by increasing contractions per day. Thus, FES should be considered in critical care units, rehabilitation centers and nursing facilities when patients are unable or reluctant to exercise.

Effects of a combined protein and antioxidant supplement on recovery of muscle function and soreness following eccentric exercise

BACKGROUND

An acute bout of eccentric contractions (ECC) cause muscle fiber damage, inflammation, impaired muscle function (MF) and muscle soreness (MS). Individually, protein (PRO) and antioxidant (AO) supplementation may improve some aspects of recovery from ECC, though have yet to be combined. We sought to determine if combined PRO and AO supplementation (PRO + AO) improves MS and MF following damaging ECC over PRO alone.

METHODS

Sixty sedentary college-aged males participated in a randomized, single-blind, parallel design study of peak isometric torque (PIMT), peak isokinetic torque (PIKT), thigh circumference (TC), and muscle soreness (MS) of knee extensor muscles measured at baseline, immediately after and 1, 2, 6, and 24 h after completion of 100 maximal ECC. Immediately, 6 h, and 22 h post-ECC, participants consumed either: carbohydrate control (CHO; n = 14), PRO (n = 16), or PRO + AO (n = 17).

RESULTS

At baseline MS, TC, MF, macro- and micro-nutrient intakes, and total work during the ECC were not different between groups (p > 0.05). PIMT and PIKT (both -25%∆), TC (~1%∆) and MS (~35%∆) all changed with time (p < 0.05). We observed a group by time effect for PIKT (PRO + AO and PRO > CHO, p < 0.05). At 24 h post ECC, there was a trend towards improved relative PIMT (~11%) and PIKT (~17%) for PRO + AO (~17%) and PRO (~11%) compared to CHO. An interaction indicated PRO + AO had lowest MS over time (PRO + AO > PRO & CHO, p < 0.05).

CONCLUSIONS

Our results suggest PRO facilitates recovery of muscle function within 24 h following ECC, and addition of AO ameliorates MS more than PRO or CHO alone.

Inflammaging and Skeletal Muscle: Can Protein Intake Make a Difference?

Inflammaging is the chronic low-grade inflammatory state present in the elderly, characterized by increased systemic concentrations of proinflammatory cytokines. It has been shown that inflammaging increases the risk of pathologic conditions and age-related diseases, and that it also has been associated with increased skeletal muscle wasting, strength loss, and functional impairments. Experimental evidence suggests that the increased concentrations of proinflammatory cytokines and primary tumor necrosis factor α observed in chronic inflammation lead to protein degradation through proteasome activation and reduced skeletal muscle protein synthesis (MPS) via protein kinase B/Akt downregulation. Dairy and soy proteins contain all the essential amino acids, demonstrate sufficient absorption kinetics, and include other bioactive peptides that may offer nutritional benefits, in addition to those of stimulating MPS. Whey protein has antioxidative effects, primarily because of its ability to enhance the availability of reduced glutathione and the activity of the endogenous antioxidative enzyme system. Soy protein and isoflavone-enriched soy protein, meanwhile, may counteract chronic inflammation through regulation of the nuclear transcription factor κB signaling pathway and cytokine production. Although evidence suggests that whey protein, soy protein, and isoflavone-enriched soy proteins may be promising nutritional interventions against the oxidative stress and chronic inflammation present in pathologic conditions and aging (inflammaging), there is a lack of information about the anabolic potential of dietary protein intake and protein supplementation in elderly people with increased systemic inflammation. The antioxidative and anti-inflammatory effects, as well as the anabolic potential of protein supplementation, should be further investigated in the future with well-designed clinical trials focusing on inflammaging and its associated skeletal muscle loss.

Effect of protein quality on recovery after intense resistance training

PURPOSE

The present study investigated the effects of high- versus low-quality protein supplementation on the regain of exercise performance during recovery from a period of high-intensity resistance training.

METHODS

In a diet-controlled crossover study, 12 resistance-trained participants performed two identical training periods, with each training period including four sessions of high-intensity resistance exercise during 5 days, while receiving either high- or low-quality protein. Prior to and at 3, 24 and 48 h after the training periods, performance was evaluated in knee extensor and flexor isometric maximal voluntary contraction (MVC), counter-movement jumping height (CMJ), and peak and mean anaerobic power. In addition, prior to and at 48 h after the training periods, performance in time-to-exhaustion at 70 % of VO_2max (TTE) was evaluated.

RESULTS

After the intense training periods, decrements in the order of 4-24 % were observed for MVC_ext, CMJ, mean anaerobic power, and TTE. In particular for TTE, this decrement in exercise performance did not attain full recovery at 48 h post-exercise. The regain of exercise performance was not dictated by type of protein supplement.

CONCLUSION

The regain of muscle strength as well as anaerobic or aerobic performances were not markedly influenced by the type of protein supplement.

Skeletal muscle regeneration and impact of aging and nutrition

After skeletal muscle injury a regeneration process takes place to repair muscle. Skeletal muscle recovery is a highly coordinated process involving cross-talk between immune and muscle cells. It is well known that the physiological activities of both immune cells and muscle stem cells decline with advancing age, thereby blunting the capacity of skeletal muscle to regenerate. The age-related reduction in muscle repair efficiency contributes to the development of sarcopenia, one of the most important factors of disability in elderly people. Preserving muscle regeneration capacity may slow the development of this syndrome. In this context, nutrition has drawn much attention: studies have demonstrated that nutrients such as amino acids, n-3 polyunsaturated fatty acids, polyphenols and vitamin D can improve skeletal muscle regeneration by targeting key functions of immune cells, muscle cells or both. Here we review the process of skeletal muscle regeneration with a special focus on the cross-talk between immune and muscle cells. We address the effect of aging on immune and skeletal muscle cells involved in muscle regeneration. Finally, the mechanisms of nutrient action on muscle regeneration are described, showing that quality of nutrition may help to preserve the capacity for skeletal muscle regeneration with age.

Potential Role of Omega-3 Fatty Acids on the Myogenic Program of Satellite Cells

Skeletal muscle loss is associated with aging as well as pathological conditions. Satellite cells (SCs) play an important role in muscle regeneration. Omega-3 fatty acids are widely studied in a variety of muscle wasting diseases; however, little is known about their impact on skeletal muscle regeneration. The aim of this review is to evaluate studies examining the effect of omega-3 fatty acids, α-linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid on the regulation of SC proliferation and differentiation. This review highlights mechanisms by which omega-3 fatty acids may modulate the myogenic program of the stem cell population within skeletal muscles and identifies considerations for future studies. It is proposed that minimally three myogenic transcriptional regulatory factors, paired box 7 (Pax7), myogenic differentiation 1 protein, and myogenin, should be measured to confirm the stage of SCs within the myogenic program affected by omega-3 fatty acids.

Satellite cells in human skeletal muscle plasticity

Skeletal muscle satellite cells are considered to play a crucial role in muscle fiber maintenance, repair and remodeling. Our knowledge of the role of satellite cells in muscle fiber adaptation has traditionally relied on in vitro cell and in vivo animal models. Over the past decade, a genuine effort has been made to translate these results to humans under physiological conditions. Findings from in vivo human studies suggest that satellite cells play a key role in skeletal muscle fiber repair/remodeling in response to exercise. Mounting evidence indicates that aging has a profound impact on the regulation of satellite cells in human skeletal muscle. Yet, the precise role of satellite cells in the development of muscle fiber atrophy with age remains unresolved. This review seeks to integrate recent results from in vivo human studies on satellite cell function in muscle fiber repair/remodeling in the wider context of satellite cell biology whose literature is largely based on animal and cell models.

Pericyte response to contraction mode-specific resistance exercise training in human skeletal muscle

Skeletal muscle satellite cells (SCs) are important for muscle repair and hypertrophy in response mechanical stimuli. Neuron-glial antigen 2-positive (NG2(+)) and alkaline phosphatase-positive (ALP(+)) pericytes may provide an alternative source of myogenic progenitors and/or secrete paracrine factors to induce Pax7(+) SC proliferation and differentiation. The purpose of this study was to investigate NG2(+) and ALP(+) cell quantity, as well as SC content and activation, in human skeletal muscle following prolonged concentric (Conc) or eccentric (Ecc) resistance training. Male subjects engaged in unilateral resistance training utilizing isolated Ecc or Conc contractions. After 12 wk, muscle biopsies were analyzed for NG2(+) and ALP(+) pericytes, total Pax7(+) SCs, activated SCs (Pax7(+)MyoD(+)), and differentiating myogenic cells (Pax7(-) MyoD(+)). NG2(+) cells localized to CD31(+) vessels and the majority coexpressed ALP. NG2(+) pericyte quantity decreased following both Conc and Ecc training (P < 0.05). ALP(+) pericyte quantity declined following Conc (P < 0.05) but not Ecc training. Conversely, total Pax7(+) SC content was elevated following Conc only (P < 0.001), while Pax7(+)MyoD(+) SC content was increased following Conc and Ecc (P < 0.001). Follow up analyses demonstrated that CD90(+) and platelet-derived growth factor receptor-α (PDGFRα)(+) mononuclear cell proliferation was also increased in response to both Conc and Ecc training (P < 0.01). In summary, resistance training results in a decline in pericyte quantity and an increase in mesenchymal progenitor cell proliferation, and these events likely influence SC pool expansion and increased activation observed posttraining.

Molecular and Cellular Mechanisms of Muscle Aging and Sarcopenia and Effects of Electrical Stimulation in Seniors

The prolongation of skeletal muscle strength in aging and neuromuscular disease has been the objective of numerous studies employing a variety of approaches. It is generally accepted that cumulative failure to repair damage related to an overall decrease in anabolic processes is a primary cause of functional impairment in muscle. The functional performance of skeletal muscle tissues declines during post- natal life and it is compromised in different diseases, due to an alteration in muscle fiber composition and an overall decrease in muscle integrity as fibrotic invasions replace functional contractile tissue. Characteristics of skeletal muscle aging and diseases include a conspicuous reduction in myofiber plasticity (due to the progressive loss of muscle mass and in particular of the most powerful fast fibers), alteration in muscle-specific transcriptional mechanisms, and muscle atrophy. An early decrease in protein synthetic rates is followed by a later increase in protein degradation, to affect biochemical, physiological, and morphological parameters of muscle fibers during the aging process. Alterations in regenerative pathways also compromise the functionality of muscle tissues. In this review we will give an overview of the work on molecular and cellular mechanisms of aging and sarcopenia and the effects of electrical stimulation in seniors..